Subset of cells immunopositive for neurokinin-1 receptor identified as arterial interstitial cells of Cajal in human large arteries

Developments in research on interstitial Cajal-like cells in the biliary tract

INTRODUCTION

Interstitial cells of Cajal (ICCs) are a special type of interstitial cells located in the gastrointestinal tract muscles. They are closely related to smooth muscle cells and neurons, participate in gastrointestinal motility and nerve signal transmission, and are pacemaker cells for gastrointestinal electrical activity. Research interest in ICCs has continuously grown since they were first discovered in 1893. Later, researchers discovered that they are also present in other organs, including the biliary tract, urethra, bladder, etc.; these cells were named interstitial Cajal-like cells (ICLCs), and attempts have been made to explain their relationships with certain diseases.

AREAS COVERED

This review paper summarizes the morphology, identification, classification, function, and distribution of ICLCs in the biliary tract and their relationship to biliary tract diseases.

EXPERT OPINION

Based on the function and distribution of ICLCs in the biliary tract system, ICLCs will provide a more reliable theoretical basis for the mechanisms of pathogenesis of and treatments for biliary tract diseases.

Vascular Interstitial Cells in Retinal Arteriolar Annuli Are Altered During Hypertension

Purpose

It has been suggested that arteriolar annuli localized in retinal arterioles regulate retinal blood flow acting as sphincters. Here, the morphology and protein expression profile of arteriolar annuli have been analyzed under physiologic conditions in the retina of wild-type, β-actin-Egfp, and Nestin-gfp transgenic mice. Additionally, to study the effect of hypertension, the KAP transgenic mouse has been used.

Methods

Cellular architecture has been studied using digested whole mount retinas and transmission electron microscopy. The profile of protein expression has been analyzed on paraffin sections and whole mount retinas by immunofluorescence and histochemistry.

Results

The ultrastructural analysis of arteriolar annuli showed a different cell population found between endothelial and muscle cells that matched most of the morphologic criteria established to define interstitial Cajal cells. The profile of protein expression of these vascular interstitial cells (VICs) was similar to that of interstitial Cajal cells and different from the endothelial and smooth muscle cells, because they expressed β-actin, nestin, and CD44, but they did not express CD31 and α-SMA or scarcely express F-actin. Furthermore, VICs share with pericytes the expression of NG2 and platelet-derived growth factor receptor beta (PDGFR-β). The high expression of Ano1 and high activity of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase observed in VICs was diminished during hypertensive retinopathy suggesting that these cells might play a role on the motility of arteriolar annuli and that this function is altered during hypertension.

Conclusions

A novel type of VICs has been described in the arteriolar annuli of mouse retina. Remarkably, these cells undergo important molecular modifications during hypertensive retinopathy and might thus be a therapeutic target against this disease.

Hypertension Induced Morphological and Physiological Changes in Cells of the Arterial Wall

Morphological and physiological changes in the vasculature have been described in the evolution and maintenance of hypertension. Hypertension-induced vascular dysfunction may present itself as a contributing, or consequential factor, to vascular remodeling caused by chronically elevated systemic arterial blood pressure. Changes in all vessel layers, from the endothelium to the perivascular adipose tissue (PVAT), have been described. This mini-review focuses on the current knowledge of the structure and function of the vessel layers, specifically muscular arteries: intima, media, adventitia, PVAT, and the cell types harbored within each vessel layer. The contributions of each cell type to vessel homeostasis and pathophysiological development of hypertension will be highlighted.

Telocytes: New Players in Gallstone Disease

Cholesterol gallstone disease is highly prevalent in Western countries, particularly in women and some specific ethnic groups. The mechanisms behind the formation of gallstones are not clearly understood, but gallbladder dysmotility seems to be a key factor that triggers the precipitation of cholesterol microcrystals from supersaturated lithogenic bile.Given that newly described interstitial cells, telocytes, are present in the gallbladder and they are located in close vicinity of smooth muscle cell and neural fibers possibly interfering with gallbladder motility or contractility, authors are trying to summarize the current knowledge on the role of telocytes with respect to disturbed gallbladder function in gallstone disease.

Morphological evidence of telocytes in mice aorta

BACKGROUND

Telocytes (TCs) are a novel type of interstitial cells, which have been recently described in a large variety of cavitary and noncavitary organs. TCs have small cell bodies, and remarkably thin, long, and moniliform prolongations called telopodes (Tps). Until now, TCs have been found in various loose connective tissues surrounding the arterioles, venules, and capillaries, but as a histological cellular component, whether TCs exist in large arteries remains unexplored.

METHODS

TCs were identified by transmission electron microscope in the aortic arch of male C57BL/6 mice.

RESULTS

TCs in aortic arch had small cell bodies (length: 6.06-13.02 μm; width: 1.05-4.25 μm) with characteristics of specific long (7.74-39.05 μm), thin, and moniliform Tps; TCs distributed in the whole connective tissue layer of tunica adventitia: TCs in the innermost layer of tunica adventitia, located at the juncture between media and adventitia, with their long axes oriented parallel to the outer elastic membrane; and TCs in outer layers of tunica adventitia, were embedded among transverse and longitudinal oriented collagen fibers, forming a highly complex three-dimensional meshwork. Moreover, desmosomes were observed, serving as pathways connecting neighboring Tps. In addition, vesicles shed from the surface of TCs into the extracellular matrix, participating in some biological processes.

CONCLUSIONS

TCs in aorta arch are a newly recognized complement distinct from other interstitial cells in large arteries, such as fibroblasts. And further biologically functional correlations need to be elucidated.

Role of mast cells in atherosclerosis: a classical inflammatory disease

Atherosclerosis is an inflammatory disease and hyperlipidaemia is one of the main risk factors for aging, hypertension and diabetes. Variance in plasma LDL cholesterol concentration may be associated with differences in cardiovascular disease risk and high levels of lipids are associated with increased risk of developing atherosclerosis. Macrophages, which generate pro-inflammatory cytokines, mainly interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-alpha), are deeply involved in atherosclerosis, as well as mast cells which generate several cytokines, including IL-6 and IFN-gamma, and chemokines such as eotaxin, MCP-1 and RANTES involved in monocyte recruitment and differentiation in the arterial wall. In addition, mast cells participate in lipid retention and vascular cell remodeling, and are mediators of innate and adaptive immunity during atherosclerosis. Mast cells which accumulate in the human arterial intima and adventitia during atherosclerotic plaque progression, release vasoactive and angiogenic compounds, and pro-inflammatory mediators, such as arachidonic acid metabolites, histamine, cytokines/chemokines, platelet activating factor (PAF) and proteolytic enzymes. Mast cells can be activated by pro-inflammatory stimuli, including cytokines, hypercholesterolemia, and hyperglycemia, and trigger the endothelial expression of adhesion molecules such as P-selection, vascular cell adhesion molecule-1 (VCAM-1) and chemokines which mediate the recruitment and adhesion of leukocytes. The participation of mast cells in atherosclerosis is still an enigma and it may be of therapeutic interest to clarify this process.

Novel methods for accurate identification, isolation, and genomic analysis of symptomatic microenvironments in atherosclerotic arteries

A challenge facing surgeons is identification and selection of patients for carotid endarterectomy or coronary artery bypass/surgical intervention. While some patients with atherosclerosis develop unstable plaques liable to undergo thrombosis, others form more stable plaques and are asymptomatic. Identification of the cellular signaling mechanisms associated with production of the inflammatory, hemorrhagic lesions of mature heterogenic plaques will help significantly in our understanding of the differences in microenvironment associated with development of regions susceptible to rupture and thrombosis and may help to predict the risk of plaque rupture and guide surgical intervention to patients who will most benefit. Here, we demonstrate detailed and novel methodologies for successful and, more importantly, accurate and reproducible extraction, sampling, and analysis of micro-regions in stable and unstable coronary/carotid arteries. This information can be applied to samples from other origins and so should be useful for scientists working with micro-isolation techniques in all fields of biomedical science.

Identification and functional response of interstitial Cajal-like cells from rat mesenteric artery

Cells with irregular shapes, numerous long thin filaments, and morphological similarities to the gastrointestinal interstitial cells of Cajal (ICCs) have been observed in the wall of some blood vessels. These ICC-like cells (ICC-LCs) do not correspond to the other cell types present in the arterial wall: smooth muscle cells (SMCs), endothelial cells, fibroblasts, inflammatory cells, or pericytes. However, no clear physiological role has as yet been determined for ICC-LCs in the vascular wall. The aim of this study has been to identify and characterize the functional response of ICC-LCs in rat mesenteric arteries. We have observed ICC-LCs and identified them morphologically and histologically in three different environments: isolated artery, freshly dispersed cells, and primary-cultured cells from the arterial wall. Like ICCs but unlike SMCs, ICC-LCs are positively stained by methylene blue. Cells morphologically resembling methylene-blue-positive cells are also positive for the ICC and ICC-LC markers α-smooth muscle actin and desmin. Furthermore, the higher expression of vimentin in ICC-LCs compared with SMCs allows a clear discrimination between these two cell types. At the functional level, the differences observed in the variations of cytosolic free calcium concentration of freshly dispersed SMCs and ICC-LCs in response to a panel of vasoactive molecules show that ICC-LCs, unlike SMCs, do not respond to exogenous ATP and [Arginine](8)-vasopressin.

Identification of telocytes in the lamina propria of rat duodenum: transmission electron microscopy

Recently the new term 'telocytes' has been proposed for cells formerly known as interstitial Cajal-like cells. In fact, telocytes are not really Cajal-like cells, they being different from all other interstitial cells by the presence of telopodes, which are cell-body prolongations, very thin, extremely long with a moniliform aspect. The identification of these cells is based on ultrastructural criteria. The presence of telocytes in others organs was previously documented. We reported for the first time, an ultrastructural study of telocytes in the lamina propria of rat duodenum. Our findings show that typical telocytes are present in the rat duodenum. Telocytes are located in the lamina propria, immediately below mucosal crypts. Telopodes frequently establish close spatial relationships with immune cells, blood vessels and nerve endings. On the basis of their distribution and morphology, we suggest that these cells may be involved in immune response and in our opinion, it may be possible that different locations of telocytes could be associated with different roles.

TELOCYTES - a case of serendipity: the winding way from Interstitial Cells of Cajal (ICC), via Interstitial Cajal-Like Cells (ICLC) to TELOCYTES

Ramon y Cajal discovered a particular cell type in the gut, which he named ‘interstitial neurons’ more that 100 years ago. In the early 1970s, electron microscopy/electron microscope (EM) studies showed that indeed a special interstitial cell type corresponding to the cells discovered by Cajal is localized in the gut muscle coat, but it became obvious that they were not neurons. Consequently, they were renamed ‘interstitial cells of Cajal’ (ICC) and considered to be pace-makers for gut motility. For the past 10 years many groups were interested in whether or not ICC are present outside the gastrointestinal tract, and indeed, peculiar interstitial cells were found in: upper and lower urinary tracts, blood vessels, pancreas, male and female reproductive tracts, mammary gland, placenta, and, recently, in the heart as well as in the gut. Such cells, now mostly known as interstitial Cajal-like cells (ICLC), were given different and confusing names. Moreover, ICLC are only apparently similar to canonical ICC. In fact, EM and cell cultures revealed very particular features of ICLC, which unequivocally distinguishes them from ICC and all other interstitial cells: the presence of 2–5 cell body prolongations that are very thin (less than 0.2 μm, under resolving power of light microscopy), extremely long (tens to hundreds of μm), with a moniliform aspect (many dilations along), as well as caveolae. Given the unique dimensions of these prolongations (very long and very thin) and to avoid further confusion with other interstitial cell types (e.g. fibroblast, fibrocyte, fibroblast-like cells, mesenchymal cells), we are proposing the term TELOCYTES for them, and TELOPODES for their prolongations, by using the Greek affix ‘telos’.

A distinct type of cell in myocardium: interstitial Cajal-like cells (ICLCs)

The existence of a novel type of interstitial cells in the heart, interstitial Cajal-like cells (ICLCs), had been described for the first time in 2005. Their identification was mainly based on ultrastructural criteria: very long (tens up to hundreds of micrometres) and moniliform prolongations, which are extremely thin (less than 0.2 μm), below the resolving power of light microscopy. Myocardial ICLCs were also identified by methylene-blue vital staining, silver impregnation, and immunoreactivity for CD 34, vimentin, CD117/c-kit, etc. Although a series of studies provided evidence for the existence of ICLCs in human atria and rat ventricles, further investigations in other laboratories, using additional techniques, are required to substantiate the consistency of these findings. Here we provide further evidence for the existence of ICLCs in human and mammalian hearts (by transmission and scanning electron microscopy, as well as confocal laser scanning microscopy). Noteworthy, we confirm that ICLCs communicate with neighbouring cells via shedding (micro)vesicles. Although these so-called ICLCs represent a distinct type of cells, different from classical interstitial cells of Cajal, or fibroblasts, their role(s) in myocardium remain(s) to be established. Several hypotheses are proposed: (i) adult stromal (mesenchymal) stem cells, which might participate in cardiac repair/remodelling; (ii) intercellular signalling (e.g. via shedding microvesicles); (iii) chemo-mechanical transducers and (iv) players in pacemaking and/or arrhytmogenesis, and so on.

Interstitial cells from rat middle cerebral artery belong to smooth muscle cell type

It is now established that non-contractile cells with thin filopodia, also called vascular interstitial cells (VICs), are constitutively present in the media of many, if not all, blood vessels. The aim of this study was to determine the type of cell lineage to which arterial VICs belong using immunocytochemical, and real-time and reverse transcription PCR (RT-PCR). Using RT-PCR, we compared gene expression profiles of single VICs and smooth muscle cells (SMCs) freshly dispersed from rat middle cerebral artery. Both VICs and SMCs expressed the SMC marker, smooth muscle myosin heavy chain (SM-MHC), but did not express fibroblast, pericyte, neuronal, mast cell, endothelial or stem cell markers. Freshly isolated VICs also did not express c-kit, which is the marker for interstitial cells of Cajal in the gastrointestinal tract. Immunocytochemical labelling of contractile proteins showed that VICs and SMCs expressed SM-MHC similarly to the same degree, but VICs in contrast to SMCs had decreased expression of alpha-SM-actin and very low or no expression of calponin. Real-time RT-PCR was consistent with immunocytochemical experiments and showed that VICs had four times lower gene expression of calponin comparing to SMCs, which may explain VICs' inability to contract. VICs had greater expression than SMCs of structural proteins such as non-muscular beta-actin and desmin. The results obtained suggest that VICs represent a subtype of SMCs and may originate from the same precursor as SMCs, but later develop filopodia and a non-contractile cell phenotype.

Mesenchymal stem cells and cardiac repair

Accumulating clinical and experimental evidence indicates that mesenchymal stem cells (MSCs) are promising cell types in the treatment of cardiac dysfunction. They may trigger production of reparative growth factors, replace damaged cells and create an environment that favours endogenous cardiac repair. However, identifying mechanisms which regulate the role of MSCs in cardiac repair is still at work. To achieve the maximal clinical benefits, ex vivo manipulation can further enhance MSC therapeutic potential. This review focuses on the mechanism of MSCs in cardiac repair, with emphasis on ex vivo manipulation.

Close relation of arterial ICC-like cells to the contractile phenotype of vascular smooth muscle cell

This work aimed to establish the lineage of cells similar to the interstitial cells of Cajal (ICC), the arterial ICC-like (AIL) cells, which have recently been described in resistance arteries, and to study their location in the artery wall. Segments of guinea-pig mesenteric arteries and single AIL cells freshly isolated from them were used. Confocal imaging of immunostained cells or segments and electron microscopy of artery segments were used to test for the presence and cellular localization of selected markers, and to localize AIL cells in intact artery segments. AIL cells were negative for PGP9.5, a neural marker, and for von Willebrand factor (vWF), an endothelial cell marker. They were positive for smooth muscle α-actin and smooth muscle myosin heavy chain (SM-MHC), but expressed only a small amount of smoothelin, a marker of contractile smooth muscle cells (SMC), and of myosin light chain kinase (MLCK), a critical enzyme in the regulation of smooth muscle contraction. Cell isolation in the presence of latrunculin B, an actin polymerization inhibitor, did not cause the disappearance of AIL cells from cell suspension. The fluorescence of basal lamina protein collagen IV was comparable between the AIL cells and the vascular SMCs and the fluorescence of laminin was higher in AIL cells compared to vascular SMCs. Moreover, cells with thin processes were found in the tunica media of small resistance arteries using transmis-sion electron microscopy. The results suggest that AIL cells are immature or phenotypically modulated vascular SMCs constitutively present in resistance arteries.

Interstitial Cajal-like cells in human gallbladder

We describe here an interstitial Cajal-like cell type (ICLC) in human gallbladder, resembling the archetypal enteric interstitial cells of Cajal. Gallbladder ICLC were demonstrated in fresh preparations (tissue cryosections) using methylene-blue, and fixed specimens in Epon semi-thin sections stained with toluidine blue or transmission electron microscopy (TEM). The positive diagnosis of gallbladder ICLC was further verified by immunohistochemistry: CD117/c-kit, CD34, and another 16 antigens: vimentin, desmin, nestin, alpha-smooth muscle actin, NK-1, S-100, PGP-9.5, tau protein, chromogranin A, NSE, GFAP, CD1a, CD62-P, CD68, estrogen and progesterone receptors. Double immunostaining was performed for CD117, CD34 and CD117 and nestin, respectively. In fresh specimens, the spatial density of gallbladder ICLC was 100-110 cells/mm(2). ICLC mainly appeared beneath the epithelium and in muscularis (about 7%, and approximately 5%, respectively). In toto, ICLC represent in gallbladder approximately 5.5% of subepithelial cells. TEM showed that diagnostic criteria were fulfilled by ICLC. Moreover, TEM indicated that the main ultrastructural distinctive feature for ICLC, the cell processes, develop into the characteristic shape at a relatively early stage of development. It remains to be established if, in humans, ICLC are involved in gallbladder (dis)functions (e.g. pace-making, secretion (auto-, juxta- and/or paracrine), intercellular signaling, or stone formation).

Interstitial Cajal-like cells in human uterus and fallopian tube

Recently, parallels have been drawn between enteric interstitial cells of Cajal (ICC) and similar cells outside the gut-interstitial Cajal-like cells (ICLC). This article reviews our laboratory findings on ICLC in the female reproductive tract. Since the morphology and function of ICLC are still a subject of debate, our purpose was to investigate whether ICLC are present in the fallopian tube and/or uterus, and if they share ultrastructural and immunohistochemical (IHC) features and/or functional roles. We studied ICLC presence in the human fallopian tube and myometrium primarily by light microscopy, and then by transmission electron microscopy (TEM), in tissue samples and at a single cell level. Taking advantage of our ICLC studies of several organs (pancreas, mammary gland, myocardium), we assembled a set of criteria, derived from ultrastructural features of ICLC, called "platinum standard." Besides the putative pacemaker function, ICLC might have other physiological roles, depending on tissue type (e.g., intercellular signaling, immune surveillance, steroid sensors). Consequently, there is a great urge for a conceptual framework that could allow a better understanding, from a functional point of view, and more so, as the ICLC processes are the longest cellular prolongations (except neurons).

Role of intracellular stores in the regulation of rhythmical [Ca2+]i changes in interstitial cells of Cajal from rabbit portal vein

Interstitial cells of Cajal (ICCs) freshly isolated from rabbit portal vein and loaded with the Ca(2+)-sensitive indicator fluo-3 revealed rhythmical [Ca(2+)](i) changes occurring at 0.02-0.1 Hz. Each increase in [Ca(2+)](i) originated from a discrete central region of the ICC and propagated as a [Ca(2+)](i) wave towards the cell periphery, but usually became attenuated before reaching the ends of the cell. In about 40% of ICCs each rhythmical change in [Ca(2+)](i) consisted of an initial [Ca(2+)](i) increase (phase 1) followed by a faster rise in [Ca(2+)](i) (phase 2) and then a decrease in [Ca(2+)](i) (phase 3); the frequency correlated with the rate of rise of [Ca(2+)](i) during phase 1, but not with the peak amplitude. Rhythmical [Ca(2+)](i) changes persisted in nicardipine, but were abolished in Ca(2+)-free solution as well as by SK&F96365, cyclopiazonic acid, thapsigargin, 2-APB, xestospongin C or ryanodine. Intracellular Ca(2+) stores visualised with the low-affinity Ca(2+) indicator fluo-3FF were found to be enriched with ryanodine receptors (RyRs) detected with BODIPY TR-X ryanodine. Rhythmical [Ca(2+)](i) changes originated from a perinuclear S/ER element showing the highest RyR density. Immunostaining with anti-TRPC3,6,7 antibodies revealed the expression of these channel proteins in the ICC plasmalemma. This suggests that these rhythmical [Ca(2+)](i) changes, a key element of ICC pacemaking activity, result from S/ER Ca(2+) release which is mediated via RyRs and IP(3) receptors and is modulated by the activity of S/ER-Ca(2+)-ATPase and TRP channels but not by L-type Ca(2+) channels.

Insights into the interstitium of ventricular myocardium: interstitial Cajal-like cells (ICLC)

We have previously described interstitial Cajal-like cells (ICLC) in human atrial myocardium. Several complementary approaches were used to verify the existence of ICLC in the interstitium of rat or human ventricular myocardium: primary cell cultures, vital stainings (e.g.: methylene blue), traditional stainings (including silver impregnation), phase contrast and non-conventional light microscopy (Epon-embedded semithin sections), transmission electron microscopy (TEM) (serial ultrathin sections), stereology, immunohistochemistry (IHC) and immunofluorescence (IF) with molecular probes. Cardiomyocytes occupy about 75% of rat ventricular myocardium volume. ICLC represent approximately 32% of the number of interstitial cells and the ratio cardiomyocytes/ICLC is about 70/1. In the interstitium, ICLC establish close contacts with nerve fibers, myocytes, blood capillaries and with immunoreactive cells (stromal synapses). ICLC show characteristic cytoplasmic processes, frequently two or three, which are very long (tens up to hundreds of microm), very thin (0.1-0.5 microm thick), with uneven caliber, having dilations, resulting in a moniliform aspect. Gap junctions between such processes can be found. Usually, the dilations are occupied by mitochondria (as revealed by Janus green B and MitoTracker Green FM) and elements of endoplasmic reticulum. Characteristically, some prolongations are flat, with a veil-like appearance, forming a labyrinthic system. ICLC display caveolae (about 1 caveola/ 1 microm cell membrane length, or 2-4% of the relative cytoplasmic volume). Mitochondria and endoplasmic reticulum (rough and smooth) occupy 5-10% and 1-2% of cytoplasmic volume, respectively. IHC revealed positive staining for CD34, EGFR and vimentin and, only in a few cases for CD117. IHC was negative for: desmin, CD57, tau, chymase, tryptase and CD13. IF showed that ventricular ICLC expressed connexin 43. We may speculate that possible ICLC roles might be: intercellular signaling (neurons, myocytes, capillaries etc.) and/or chemomechanical sensors. For pathology, it seems attractive to think that ICLC might participate in the process of cardiac repair/remodeling, arrhythmogenesis and, eventually, sudden death.

Relationships between neurokinin receptor-expressing interstitial cells of Cajal and tachykininergic nerves in the gut

The so-called interstitial cells of Cajal (ICC) are distributed throughout the muscle coat of the alimentary tract with characteristic intramural location and species-variations in structure and staining. Several ICC sub-types have been identified: ICC-DMP, ICC-MP, ICC-IM, ICC-SM. Gut motility is regulated by ICC and each sub-type is responsible for the electrical activities typical of each gut region and/or muscle layer. The interstitial position of the ICC between nerve endings and smooth muscle cells has been extensively considered. Some of these nerve endings contain tachykinins. Three distinct tachykinin receptors (NK1r, NK2r and NK3r) have been demonstrated by molecular biology. Each of them binds with different affinities to a series of tachykinins (SP, NKA and NKB). In the ileum, SP-immunoreactive (SP-IR) nerve fibers form a rich plexus at the deep muscular plexus (DMP), distributed around SP-negative cells, and ICC-DMP intensely express the SP-preferred receptor NK1r; conversely a faint NK1r-IR is detected on the ICC-MP and mainly after receptor internalization was induced by agonists. ICC-IM are never stained in laboratory mammals, while those of the human antrum are NK1r- IR. RT-PCR conducted on isolated ileal ICC-MP and gastric ICC-IM showed that these cells express NK1r and NK3r. Colonic ICC, except those in humans, do not express NK1r-IR, at least in resting conditions. Outside the gut, NK1r-IR cells were seen in the arterial wall and exocrine pancreas. In the mouse gut only, NK1r-IR is present in non-neuronal cells located within the intestinal villi, so-called myoid cells, which are c-kit-negative and alpha-smooth muscle actin-positive. Immunohistochemistry and functional studies confirmed that ICC receive input from SP-IR terminals, with differences between ICC sub-types. In the rat, very early after birth, NK1r is expressed by the ICC-DMP and SP by the related nerve varicosities. Studies on pathological conditions are few and those on mutant strains practically absent. It has only been reported that in the inflamed ileum of rats the NK1r-IR ICC-DMP disappear and that at the peak of inflammatory conditions ICC-MP are NK1r-IR. In the ileum of mice with a mutation in the W locus, ICC-DMP were seen to express c-kit-IR but not NK1-IR, and SP-IR innervation seems unchanged. In summary, there are distinct ICC populations, each of them under a different tachykininergic control and, likely, having different functions. Further studies are recommended at the aim of understanding ICC involvement in modulating/transmitting tachykininergic inputs.

Interstitial Cajal-like cells (ICLC) in atrial myocardium: ultrastructural and immunohistochemical characterization

We have previously reported (Hinescu & Popescu, 2005) the existence of interstitial Cajal-like cells (ICLC), by transmission electron microscopy, in human atrial myocardium. In the present study, ICLC were identified with non-conventional light microscopy (NCLM) on semi-thin sections stained with toluidine blue and immunohistochemistry (IHC) for CD117/c-kit, CD34, vimentin and other additional antigens for differential diagnosis. Quantitatively, on semi-thin sections, ICLC represent about 1-1.5% of the atrial myocardial volume (vs. approximately 45% working myocytes, approximately 2% endothelial cells, 3-4% for other interstitial cells, and the remaining percentage: extracellular matrix). Roughly, there is one ICLC for 8-10 working atrial myocytes in the intercellular space, beneath the epicardium, with a characteristic (pyriform, spindle or triangular) shape. These ICLC usually have 2-3 definitory processes, emerging from cell body, which usually embrace atrial myocytes (260 nm average distance plasmalemma/sarcolemma) or establish close contact with nerve fibers or capillaries (approximately 420 nm average distance to endothelial cells). Cell prolongations are characteristic: very thin (mean thickness = 0.15+/-0.1 microm), very long for a non-nervous cell (several tens of microm) and moniliform (uneven caliber). Stromal synapses between ICLC and other interstitial cells (macrophages) were found (e.g. in a multicontact type synapse, the average synaptic cleft was approximately 65 nm). Naturally, the usual cell organelles (mitochondria, smooth and rough endoplasmic reticulum, intermediate filaments) are relatively well developed. Caveolae were also visible on cell prolongations. No thick filaments were detected. IHC showed that ICLC were slightly and inconsistently positive for CD117/c-kit, variously co-expressed CD34 and EGF receptor, but appeared strongly positive for vimentin, along their prolongations. Some ICLC seemed positive for a-smooth muscle actin and tau protein, but were negative for nestin, desmin, CD13 and S-100. In conclusion, we provide further evidence of the existence of ICLC in human atrial myocardium, supporting the possible ICLC role in pacemaking, secretion (juxta- and/or paracrine), intercellular signaling (neurons and myocytes). For pathology, ICLC might as well be 'players' in arrhythmogenesis and atrial remodeling.